Toxic algae update - a tale of contrast

  • Published Date 08 Mar 2019

Toxic algae levels this week are on the increase across the region, but especially in Wairarapa's Ruamahanga catchment where some sites are nearing, or are at, safety guideline levels.

Heavy rainfall is predicted for western parts of the region, which should help keep toxic algae in check. Greater Wellington is urging people not to swim for 48 hours following heavy rainfall, due to the risk of illness from pathogens that may washed into local rivers and streams.  

Unfortunately, no heavy rain is predicted for Wairarapa so toxic algae levels are likely to remain high in some areas.          

Current toxic algae status

  • Kāpiti Coast: toxic algae in the Otaki River have increased to ~10% riverbed cover south of SH1. In the Waikanae River toxic algal levels are ~5% riverbed cover south of SH1. These fall within safety guidelines, but the rain effect will make the water unsafe for swimming for 48 hours.
  • Hutt Catchment: toxic algae levels remain low in the Hutt River, ~5% riverbed cover at Silverstream Bridge was the highest level observed this week. No toxic algae were observed at the Pakuratahi River at Kaitoke Regional Park. The rain effect will make the water unsafe for swimming for 48 hours.
  • Ruamahanga Catchment: toxic algae levels are at ~20% riverbed cover (right on guideline levels) at both the Ruamahanga River at Double Bridges and Waingawa River at South Road monitoring sites. Care should be taken at these locations.

The Waipoua River at Colombo Road is ~5% riverbed cover.

The Ruamahanga catchment sites will be reassessed on Monday 11 March to see if stronger warnings are needed.

Be careful out there

  • The best thing you can do to keep yourself, your kids, and your pets safe is to know what toxic algae looks like and avoid it
  • Toxic algae forms velvety or leathery looking mats on rocks in the riverbed and are
  • They are blackish/brown to dark green in colour
  • Dogs love the musty, earthy  smell of toxic algae mats and will try to eat them if given the chance
  • If you're not sure, it's best to play it safe and keep your dog on a lead.

For more information, visit our webpage.

Updated September 20, 2023 at 12:16 PM

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